DEM simulation on the AE characteristics and mechanical behaviour of soft-hard composite rock-like materials with parallel fissures subjected to uniaxial compression

The mechanical behaviour of the multi fractured soft-hard composite rock mass is not clear, which may bring certain difficulties to engineering management. Understanding the crack behaviour and acoustic emission characteristics of the fractured soft-hard composite rock mass will provide some help for engineering practice. In this paper, DEM simulation was used to study the influence of the fissure dip angle (α) and the rock bridge dip angle (β) on the acoustic emission characteristics, crack behaviour, displacement field, and stress field evolution of the soft-hard composite rock mass with three parallel fissures. The results show that the peak stress and elastic modulus of S group are always smaller than that of H group. As α increases, the ratio of shear AE events both before and after the peak gradually increases. Samples with larger α exhibit more intense acoustic emission activity. The b value of the S group is always lower than those of the H group. The b value of both samples groups increases and then decreases with the increase of α, reaching the minimum value when α is 45°. The b value of the H group fluctuates in an S-shape as β increases. In contrast, the b value of the S group first increases and then decreases with the increase of β, peaking at 90° for β. Due to the limitations on the direction and magnitude of particle displacement, there are differences in the types of rock bridge cracks in the S and H group samples. Larger α and β tend to mitigate the concentration of tensile stress, leading to an expanded area of tensile stress coverage. The S group samples are more sensitive to this mitigating effect.